Semiconductor Package Structure Having Enhanced Thermal Dissipation Characteristics

ABSTRACT

In an exemplary embodiment, a packaged device having enhanced thermal dissipation characteristics includes a semiconductor chip having a major current carrying or heat generating electrode. The semiconductor chip is oriented so that the major current carrying electrode faces the top of the package or away from the next level of assembly. The packaged device further includes a conductive clip for coupling the major current carrying electrode to a next level of assembly, and a heat spreader device formed on or integral with the conductive clip. A portion of the heat spreader device may be optionally exposed.

BACKGROUND OF THE INVENTION

The present invention relates in general to semiconductor devicepackaging and, more particularly, to semiconductor components housed inpackages having improved heat transfer characteristics.

There is a continuing demand for electronic systems with a higherfunctionality and smaller physical size. With this demand, there areseveral challenges that face electronic component designers andmanufacturers. Such challenges include the management of heat generatedby power semiconductor devices, which are typically arranged closelytogether or next to sensitive logic circuits on electronic circuitboards.

In current configurations, plastic encapsulated devices are commonlyused. One problem with plastic packages is that the thermal conductivityout of a package is often limited by the plastic molding material. As aresult, the majority of the heat generated by the semiconductor deviceis transferred through the lower part of the package next to the printedcircuit board. Because the printed circuit boards are becoming moredensely populated, the boards cannot properly dissipate or handle largeamounts of heat. When this happens, the boards can warp, which can causedamage to both the board and the components on the board. In addition,the heat itself can damage other components on the printed circuit boardor the materials that make up the board.

In view of this problem, the semiconductor industry is migrating topackages that have the capability of transferring heat out through thetop of the package instead of through the printed circuit boards.However, current designs have several disadvantages including exposed ornon-passivated semiconductor devices and non-standard manufacturingtechniques. These disadvantages affect reliability and increasemanufacturing costs and cycle time. Additionally, such designs typicallyplace the device in major current carrying electrode down orientation(e.g., “source-down”) so that heat continues to be transferred throughthe printed circuit boards, which is an inefficient mode of heattransfer.

Accordingly, a need exists for semiconductor packages that have enhancedthermal dissipation characteristics without detrimentally impactingdevice reliability, manufacturing cycle time, and cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an enlarged cross-sectional view of a packagestructure according to an embodiment of the present invention;

FIG. 2 illustrates an enlarged cross-sectional view of a packagestructure according to a second embodiment of the present invention;

FIG. 3 illustrates an enlarged cross-sectional view of a packagestructure according to a third embodiment of the present invention;

FIGS. 4-7 illustrate views of alternative heat spreader structures foruse with the present invention;

FIGS. 8 a-b illustrate views of further heat spreader structures for usewith the present invention;

FIG. 9 illustrates an enlarged cross-sectional view of a packagestructure according to a fourth embodiment of the present invention;

FIG. 10 illustrates an enlarged cross-sectional view of a packagestructure according to a fifth embodiment of the present invention;

FIG. 11 illustrates an enlarged cross-sectional view of a packagestructure according to a another embodiment of the present invention;

FIG. 12 illustrates an enlarged cross-sectional view of a packagestructure according to a further embodiment of the present invention;

FIG. 13 illustrates an enlarged cross-sectional view of a packagestructure according to a still further embodiment of the presentinvention; and

FIGS. 14 a-d illustrate partial top views of portions of alternativeheat spreaders in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

For ease of understanding, elements in the drawing figures are notnecessarily drawn to scale, and like element numbers are used whereappropriate throughout the various figures. Although the invention isdescribed using a leadless package embodiments, those skilled in the artwill recognize that the present invention is applicable to other typesof packages as well, particularly those where enhanced heat transfercharacteristics are important.

FIG. 1 shows an enlarged cross-sectional view of a packagedsemiconductor structure, leadless package, leadless packaged device orpackage 10 having enhanced thermal dissipation or heat transfercharacteristics in accordance with the present invention. Packageddevice 10 includes a conductive substrate or lead frame 11, whichincludes a flag, plate, or die attach portion 13 and a lead, terminal,connection, or pad portion 14. Lead frame 11 comprises, for example,copper, a copper alloy (e.g., TOMAC 4, TAMAC 5, 2ZFROFC, or CDA194), acopper plated iron/nickel alloy (e.g., copper plated Alloy 42), platedaluminum, plated plastic, or the like. Plated materials include copper,silver, multi-layer plating such nickel-palladium and gold. Flag portion13 and pad portion 14 are used to connect or couple to bonding pads on anext level of assembly such as a printed circuit board.

Package 10 further includes an electronic chip or semiconductor device17, which is attached to flag 13 using a die attach layer 19.Semiconductor device 17 comprises, for example, a power MOSFET device, abipolar transistor, an insulated gate bipolar transistor, a thyristor, adiode, an analog or digital integrated circuit, a sensor, a passivecomponent, or other electronic device. In an exemplary embodiment,semiconductor device 17 comprises a power MOSFET device including asource, an up-source, or major current carrying electrode or terminal21, a drain, down-drain, or current carrying electrode or terminal 23,and a gate or control electrode (not shown). Source electrode 21comprises, for example, a solderable top metal, aluminum, an aluminumalloy, or the like. Drain electrode 23 typically comprises a solderablemetal layer or layers such as TiNiAg, CrNiAu, or the like. In accordancewith the present invention, semiconductor chip 17 is in a major currentcarrying electrode or source electrode “up” or up-source configuration.That is, the major heat generating electrode (e.g., electrode 21) ofsemiconductor chip 17 is oriented away from or opposite from the side ofpackage 10 that will be attached to the next level assembly. Thisorientation promotes heat transfer out of top surface 28 of package 10,instead of through the next level of assembly or through the chipitself.

A conductive attachment structure or conductive clip or strap 31 iscoupled to source electrodes 21 and pad portion 14 to provide anelectrical path between semiconductor chip 17 and pad portion 14.Conductive clip 31 is attached to electrodes 21 using, for example, anattachment layer 24. Suitable materials for attachment layer 24 includesolder, or high conductivity epoxy materials, such as a CEL9750HFLO(AL3) or a CEL9210 HFLO(AL2) epoxy available from Hitachi Chemical,or an EMF 760 a epoxy available from Sumitomo Plastics America. Similarmaterials are used, for example, to further attach conductive clip 31 topad portion 14.

A heat spreader device, a thermal dissipation structure or thermallyconductive device or clip or strap 32 is integrated, formed with,attached, or coupled (directly or indirectly) to conductive clip 31. Inan exemplary embodiment, heat spreader 32 is attached to conductive clip31 using an attachment layer 34. In an exemplary embodiment, heatspreader 32 comprises a bridge-like shape. Clip 31 and heat spreaderdevice 32 comprise, for example, rigid copper or a copper alloy and maybe optionally plated with silver for either solder attachment orconductive epoxy attachment. Alternatively, heat spreader device 32comprises a flexible or compliant material as described below. Suitablematerials for attachment layer 34 include solder, or high conductivityepoxy materials, such as a CEL9750 HFLO(AL3) or a CEL9210 HFLO(AL2)epoxy available from Hitachi Chemical, or an EMF 760 a epoxy availablefrom Sumitomo Plastics America. Clip 31 is attached to pad portion 14using a solder, conductive epoxy, or the like.

In accordance with the present invention, clip 31 is designed to have amaximum surface area to attach to electrode 21, which reduces theelectrical resistance of package 10. Integrated heat spreader structure32 is used, among other things, to enhance the transfer of heat thatmajor current carrying electrode 21 generates out the top of package 10.This lowers thermal resistance and improves the overall performance andreliability of package 10.

An encapsulating or passivating layer 29 is formed over lead frame 11,at least a portion of semiconductor chip 17, at least a portion ofattachment structure 31, and at least a portion of heat spreaderstructure 32 using a single cavity or overmolding process. In theembodiment shown in FIG. 1, a portion 322 of heat spreader structure 32is optionally exposed or not covered by encapsulating layer 29 tofurther improve thermal dissipation. Alternatively and as shown in FIG.9, encapsulating layer 29 covers heat spreader structure 32. In afurther embodiment, an optional thermally conductive but electricallyinsulative layer 280 (e.g., thermal grease or the like) is formed overthe top surface 28 of package 10. Layer 280 is shown as a partial layerin FIG. 1 because it is optional. It is understood that when used, layer280 preferably covers the entire top surface 28.

In a preferred method for forming package 10 and after attachmentstructure 31 and heat spreader structure 32 are attached, formed orintegrated, the assembly is placed in a molding apparatus so thatportions 322 contact or adjoin a surface of the mold cavity. The surfaceof the mold cavity acts as a mask to prevent encapsulating material 29from covering portions 322 of heat spreader structure 32. It isunderstood that this method is suitable for forming the other packageembodiments having exposed heater spreader portions described herein.

In an exemplary embodiment, encapsulating layer 29 comprises a highthermal conductivity mold compound. Preferably, encapsulating layer 29comprises a mold compound having a thermal conductivity greater thanabout 3.0 Watts/MK. Suitable high conductivity mold compounds areavailable from Sumitomo Plastics America of Santa Clara, Calif. (e.g.,EME A700 series) and Hitachi Chemical of Santa Clara, Calif. (e.g., aCEL 9000 series mold compound).

Attachment structure 31 and heat spreader structure 32 are shown withone or more optional mold lock features or notches 39, which are used toprovide better adhesion between encapsulating layer 29, attachmentstructure 31, and/or heat spreader structure 32. More or fewer notches39 may be used. It is understood that notches 39 are optionallyincorporated with any of the attachment/heat spreader structuresdescribed herein.

FIG. 2 shows an enlarged cross-sectional view of a packagedsemiconductor structure, leadless package, leadless packaged device, orpackage 20 according to a second embodiment of the present invention.Package 20 does not include lead frame 11, but instead electrode orterminal 23 of semiconductor chip 17 is exposed to directly couple to anext level of assembly. By eliminating lead frame 11, a thinner packageprofile is achieved. An attachment structure or conductive clip 310 isattached to source electrode 21 using attachment layer 24, and a distalend 311 of conductive clip 310 is shaped to also couple to a next levelof assembly. In this embodiment, the heat spreader comprises a ribbonbond structure 320.

Ribbon bond structure 320 refers to a flexible rectangular shapedconductor having a width greater than its thickness. Suitable materialsfor ribbon bond structure 320 include gold, aluminum, silver, palladium,copper, or the like. Attachment of ribbon bond 320 to attachmentstructure 310 is achieved using, for example, wedge bonding. In oneembodiment, ribbon bond structure 320 is formed having a thickness ofabout twenty five microns and a width of about seventy five microns.Alternatively, ribbon bond structure 320 is typically formed to athickness of about six microns to fifty microns and a width of aboutfifty microns to fifteen hundred microns wide. In the embodiment shown,portion(s) 321 of ribbon bond structure 320 are exposed or not coveredby encapsulating layer 29 to further enhance thermal dissipation. In analternative embodiment, encapsulating layer 29 covers ribbon bondstructure 320, but the distance between portions 321 and surface 28 areminimized to minimize thermal resistance.

FIG. 3 shows an enlarged cross-sectional view of a packagedsemiconductor structure, leadless package, leadless packaged device, orpackage 30 according to a third embodiment of the present invention.Package 30 is similar to package 10 except that in package 30 acompliant or flexible heat spreader structure 323. Heat spreaderstructure 323 comprises copper or a copper alloy and may be optionallyplated with silver for either solder attachment or conductive epoxyattachment.

Heat spreader structure 323 is “u” or horseshoe shaped, and isspring-like, resilient or accommodating in structure so that it staysexpanded or contracts under a compressive force to ensure a portion 324is exposed after molding. For example, if flag 13, semiconductor chip17, and/or clip 31 are on the lower end of the thickness tolerances,heat spreader structure 323 stays expanded to contact the mold surfaceduring molding. If flag 13, semiconductor chip 17, and/or clip are onthe upper end of the thickness tolerances, heat spreader structure 323compresses during molding to accommodate for the thicker profile.

FIGS. 4, 5 and 6 show alternative embodiments for compliant oraccommodating heat spreader structures. For example, FIG. 4 shows a sideview of a compliant elliptical or oval shaped heat spreader or clip 423,and FIG. 5 shows a compliant spring-like circular, spring, coil-like orhelical heat spreader structure 523. FIG. 6 shows a compliantsponge-like or scouring pad-like mesh or random matrix or mesh ofthermally conductive material 623. In an exemplary embodiment, mesh 623comprises a metal mesh (e.g., copper or the like). In an alternativeembodiment, mesh 623 is placed between the attachment structures andother heat spreader structures described herein to provide furtherenhanced thermal dissipation. For example, mesh 623 is added betweenclip 131 and heat spreader 32 shown in FIG. 9 to provide a second heatspreader structure. Mesh 623 is shown in part in FIG. 9 because it isoptional. It is understood that mesh 623 may alternatively substantiallyfill or partially fill the space between the attachment structure andthe other heat spreader.

FIG. 7 shows a side view of a heat spreader structure 723 including oneor more fin portions 724, which is suitable for the embodimentsdisclosed herein.

FIGS. 8 a and 8 b show side views of wire bond structures suitable forbonding to the clips shown herein (e.g., clip 31) to provide furtherheat spreader structures. FIG. 8 a shows a ball bond structure 823,which is formed on the attachment structure using conventional ballbonding techniques. FIG. 8 b shows a wedge or stitch bond structure 825,which is formed on the attachment structure using conventional wedgebonding techniques. Heat spreaders 823 and 825 comprise for example,aluminum or the like.

FIG. 9 shows an enlarged cross-sectional view of a packagedsemiconductor structure, leadless package, leadless packaged device, orpackage 40 according to a fourth embodiment of the present invention.Package 40 is similar to package 10 except that in package 40, anencapsulating layer 29 covers heat spreader structure 32 so that noportions of heat spreader structure 32 are exposed. Preferably, distance86 between heat spreader 32 and top surface 28 is minimized to minimizethermal resistance. In an exemplary embodiment, distance 86 is less thanabout 0.13 millimeters (mm). Also, package 40 includes a flat orsubstantially planar attachment structure or clip 131, which is coupledon one end to electrode 21 of semiconductor chip 17, and coupled to apad portion 141 on the other end. Additionally, in package 40, terminal23 of semiconductor chip 17 is exposed as shown for attachment to a nextlevel of assembly. As described above, package 40 is shown in withoptional mesh 623, which functions as a second or additional heatspreader.

FIG. 10 shows an enlarged cross-sectional view of a packagedsemiconductor structure, leadless package, leadless packaged device, orpackage 50 according to a fifth embodiment of the present invention.Package 50 is similar to package 10 except that in package 50 the heatspreader structure comprises a plurality of conductive sphere likeshapes or balls 326. In an exemplary embodiment, balls 326 are metalsphere shapes comprising copper, solder, gold, aluminum, metal coatedceramics, metal coated plastic, or the like, and are attached using forexample, a solder or epoxy. Alternatively, sphere like shapes 328 areformed on clip 31 using a clipped wire bond approach and comprisealuminum or the like. Preferably, portions 327 or 329 of balls 326 or328 are exposed through encapsulating layer 29 as shown to furtherenhance thermal dissipation.

Alternatively, encapsulating layer 29 covers balls 326 with balls 326remaining in proximity to the surface of package 50 to minimize thermalresistance.

FIG. 11 shows an enlarged cross-sectional view of a packagedsemiconductor structure, leadless package, leadless packaged device, orpackage 60 according to another embodiment of the present invention.Package 60 is similar to package 10 except that package 60 furtherincludes a second semiconductor chip or component 117. Second component117 is the same as or different than semiconductor chip 17. In anexemplary embodiment when semiconductor chip 17 comprises a powerMOSFET, second component 117 comprises a Schottky diode having atermination or electrode 123 coupled to clip 31. For example,termination 123 is coupled to clip 31 using an attachment layer 119.Termination 123 is electrically coupled to clip 31, or may be isolatedfrom clip 31 with electrical contact to termination 123 achieved using alaminate structure (e.g., a conductive layer separated from clip 31 byan insulating layer). Another termination or electrode 121 is coupled toanother pad portion (not shown) of package 60 using a second attachmentstructure or clip 231. In this embodiment, heat spreader structure 32spans over second component 117 for example, to save space.

FIG. 12 shows an enlarged cross-sectional view of a packagedsemiconductor structure, leadless package, leadless packaged device, orpackage 70 according to a further embodiment of the present invention.Package 70 is similar to package 10 except that in package 70,attachment structure 732 acts as a heat spreader, and a conductive plateor disc 731 couples electrode 21 to attachment structure 732 usingattachment layer 34 as described above. In an exemplary embodiment,plate 731 is designed to match the shape or outline of electrode 21 toprovide an optimized heat and electrical current spreading capability.Plate 731 can match electrode 21 without the need to modify 732 therebyimproving manufacturability. Optionally, plate 731 is formed onsemiconductor chip 17 at wafer level to further improvemanufacturability.

In the embodiment shown in FIG. 12, attachment structure 732 has acompliant or accommodating shape similar to heat spreader 323 shown inFIG. 3, which compensates for thickness tolerance variations of thevarious components. In an alternative embodiment, attachment structure732 has a shape similar to attachment structure 31 or 310 (if lead frame11 is eliminated). Attachment structure 732 and conductive plate 731comprise materials similar to those described for attachment structure31 and heat spreader 32. Attachment structure 732 includes an optionalexposed portion 733. The length of coupling portion 734 of attachmentstructure 732 can be the same as or different than the width ofconductive plate 731.

FIG. 13 shows an enlarged cross-sectional view of a packagedsemiconductor structure, leadless package, leadless packaged device, orpackage 80 according to a still further embodiment of the presentinvention. Package 80 is similar to package 10 except that conductivestructure 830 has an attachment portion or structure 831 and a heatspreader portion 832 coupled, integrated, or formed as or from a singlepiece of material. As shown in FIG. 13, heat spreader portion 832extends away from semiconductor chip 17, and is adjacent or in proximityto surface 28 of package 80. In an exemplary embodiment, a portion 833of heat spreader 832 is exposed. In an alternative embodiment, heatspreader 832 is covered. Preferably, conductive structure 830 has acompliant or accommodating shape, which compensates for thicknesstolerance variations of the various components. Conductive structure 830comprises materials similar to those described for attachment structure31 or heat spreader 32. In a further embodiment, the shape of conductivestructure 830 is inversed to be similar to the shape of attachmentstructure 732 shown in FIG. 12.

The heat spreaders shown herein may have a solid or continuous shape orform. FIGS. 14 a-d show various partial top views for alternativeshapes, portions or forms for heat spreaders 32, 321, 323,423, 723, 732,and 832. These shapes provide, among other things, enhanced adhesionbetween encapsulating layer 29 and the heater spreader portion. FIG. 14a shows a comb-like or finned shape or portion 130 a; FIG. 14 b shows ashape or checker-board shape 130 b including an opening(s) or hole(s)131; FIG. 14 c shows a saw-tooth shape or portion 130 c; and FIG. 14 dshows a heat spreader 130 d having a “c” shaped cut-out portion 135.

In summary, there has been described a package structure that includesvarious embodiments of integrated attachment/heat spreader devices,which provide, among other things, enhanced thermal dissipation or heattransfer characteristics.

1. A semiconductor package comprising: an electronic chip having a majorcurrent carrying electrode on a first surface; a conductive attachmentstructure coupled to the major current carrying electrode; a heatspreader integrated with the conductive attachment structure; and anencapsulating layer covering a portion of the electronic chip, a portionof the conductive attachment structure, and at least a portion of theheat spreader.
 2. The package of claim 1 wherein the heat spreadercomprises a compliant shape.
 3. The package of claim 2 wherein the heatspreader comprises one of a “u” shape, a coil-like shape, or anelliptical shape.
 4. The package of claim 1 wherein the encapsulatinglayer covers the heat spreader.
 5. The package of claim 1 wherein theheat spreader comprises a conductive mesh.
 6. The package of claim 1wherein the heat spreader comprises a ribbon bond.
 7. The package ofclaim 1 wherein the heat spreader comprises a plurality of sphere likeshapes.
 8. The package of claim 1 wherein the conductive contactstructure and the heat spreader comprise a single piece of material. 9.The package of claim 1 further comprising a lead frame having a flagportion and a pad portion, wherein the electronic chip is coupled to theflag portion, and wherein the conductive attachment structure is furthercoupled to the pad portion.
 10. The package of claim 1 furthercomprising a second electronic component coupled to the conductiveattachment structure.
 11. The package of claim 10 wherein the electronicchip comprises a power MOSFET, and wherein the second electroniccomponent comprises a Schottky diode.
 12. The package of claim 1 whereinthe heat spreader includes a shape that enhances the adhesion of theencapsulating layer to the heat spreader.
 13. The package of claim 1further comprising a thermally conductive and electrically insulatinglayer formed over the package.
 14. The package of claim 1 wherein theencapsulating layer comprises a material having a thermal conductivitygreater than or equal to about 3.0 Watts/mK.
 15. The package of claim 1wherein the heat spreader comprises at least one wire bond.
 16. Thepackage of claim 15 wherein the wire bond comprises a ball bond heatspreader.
 17. The package of claim 15 wherein the wire bond comprises awedge bond heat spreader.
 18. A leadless semiconductor package havingenhanced thermal dissipation comprising: a lead frame including aterminal portion; a semiconductor device having a first electrode on asurface; an attachment structure coupled to the first electrode and theterminal portion; a thermally conductive device coupled to theattachment structure; and a passivating layer covering at least aportion of the semiconductor device, at least a portion of theattachment structure, and at least a portion of the thermally conductivedevice.
 19. The package of claim 18 wherein the attachment structurecomprises a clip.
 20. The package of claim 18 wherein the thermallyconductive device comprises a compliant shape.
 21. The package of claim18 wherein the thermally conductive device comprises one of a ribbonbond, a wire bond, a clip having a bridge-like shape, a “u” shaped clip,an elliptical shaped clip, a plurality of sphere like shapes, a heatspreader having fin portions, a conductive mesh, or a coil-like heatspreader.
 22. The package of claim 18 wherein one of the attachmentstructure and the thermally conductive device includes a mold lockfeature.
 23. The package of claim 18 wherein the thermally conductivedevice includes one of a comb-like shaped portion, a portion having anopening, or a saw-tooth shaped portion.
 24. The package of claim 18wherein the passivating layer comprises a material having a thermalconductivity greater than or equal to about 3.0 Watts/mK.
 25. Thepackage of claim 18 further comprising a second semiconductor chipcoupled to the attachment structure.
 26. A electronic packagecomprising: a semiconductor die having a major current carryingelectrode; a conductive structure having an attachment portion coupledto the major current carrying electrode, wherein the conductivestructure further includes a heat spreader portion that extends awayfrom the semiconductor chip and is adjacent an upper surface of thepackage; and an encapsulating layer covering at least a portion of thesemiconductor die and at least a portion of the conductive structure.27. The electronic package of claim 26 wherein the conductive structurecomprises a compliant shape.
 28. The electronic package of claim 26further comprising a conductive plate between the conductive structureand the semiconductor die.
 29. The electronic package of claim 26further comprising a lead frame having a flag portion and a pad portion,wherein the semiconductor die is coupled to the flag portion, andwherein one end of the conductive structure is coupled to the padportion.
 30. The electronic package of claim 26 wherein thesemiconductor die comprises a power MOSFET device.
 31. The electronicpackage of claim 26 wherein the encapsulating layer comprises a materialhaving a thermal conductivity greater than or equal to about 3.0Watts/mK.
 32. The electronic package of claim 26 wherein a portion ofthe heat spreader portion is exposed to enhance thermal dissipation.